A. Basic black or clear plastic rimmed, standard lens sized, frames are inexpensive.
B. The materials and techniques used to manufacture hi-tech light weight and relatively indestructible frames with spring-loaded ear pieces are pricey.
C. "Designer Frames" - you pay for the name!
Or put another way - they charge it because people pay it!
der Brucer
Perhaps you're right. The bridge of my nose is small and I have difficulty getting a good fit. I usually buy Silouettes, which run about $150, but I can't get a comfortable fit with most other manufacturers.
I asked my optican recently why some non-prescription sunglasses are so expensive and she did give what seemed like valid reasons, but a lot of that had to do with the quality of the lens, not the frame.
BTW, Luxottica in Italy manufactures frames under a wide array of designer names. They may carry different brand names, but most are made in the same factories.